Catalyst for one-pot catalytic oxygen oxidation of primary alcohol to prepare ester, preparation method and application thereof

Abstract

This invention relates to catalysts, preparation methods, and applications for the one-pot catalytic oxidation of primary alcohols to esters using oxygen. The catalyst is a zinc-cobalt composite oxide, denoted as Zn-CoO, obtained by stepwise calcination of a Zn-doped modified ZIF-67 precursor. x The morphology is basically rhombic dodecahedral with a slightly concave surface, and the particle size is 0.8~1.2 μm. The primary alcohol as the reaction substrate is added to the reaction solvent, followed by the catalyst Zn-CoO. x The reaction involves the use of N-hydroxyphthalimide as a co-catalyst, with oxygen introduced into the solution during the reaction. The ester product is then separated after the reaction. This invention exhibits excellent catalytic performance for a variety of typical primary alcohols. The esterification yields are as follows: n-propanol oxidative esterification yield reaches 85.6%, n-butanol 97.0%, cyclohexylmethanol 89.9%, n-octanol 80.8%, and benzyl alcohol up to 96.0%. It demonstrates broad applicability and high selectivity for straight-chain aliphatic primary alcohols, cycloalkyl methanols, and aromatic primary alcohols.

Description

Technical Field

[0001] This invention relates to the field of heterogeneous catalysis and green oxidation technology, specifically to catalysts, preparation methods, and applications for the one-pot catalytic oxidation of primary alcohols with oxygen to produce esters. Background Technology

[0002] Ester compounds are a crucial class of fine chemical intermediates and bulk chemical products, widely used in food flavorings, pharmaceutical synthesis, coating additives, polymer materials and many other fields. Therefore, the development of efficient, green and economical synthesis methods for ester compounds has always been a focus of attention.

[0003] The mainstream method for preparing esters in traditional industry is the Fischer esterification reaction (Otera J, et al. Chem. Rev., 1993, 93 (4), 1449-1470), which uses carboxylic acids and alcohols as raw materials to undergo an esterification reaction under the action of strong acid catalysts such as concentrated sulfuric acid and p-toluenesulfonic acid to obtain the target ester. Although this process is technically mature, it has many unavoidable drawbacks: First, most of the carboxylic acids used as raw materials need to be prepared by the oxidation reaction of primary alcohols, and the overall production process requires two steps: "olive oxidation to carboxylic acid - carboxylic acid and alcohol esterification", which is cumbersome. Second, strong acid catalysts cause serious equipment corrosion problems. Third, the reaction process is prone to generating by-products, and the subsequent neutralization and washing processes generate a large amount of saline wastewater, resulting in high costs for waste treatment.

[0004] Compared to the traditional two-step process, the direct one-pot oxidative esterification of primary alcohols to prepare esters uses only a single primary alcohol as a raw material. Symmetrical esters are synthesized in one step through a tandem "oxidation-esterification" reaction, eliminating the need for additional carboxylic acid feedstock. This significantly shortens the process flow and greatly improves atom utilization. Among these methods, using oxygen or air as the oxidant is the most promising for industrialization due to its advantages of being inexpensive, readily available, environmentally friendly, and theoretically producing only water as a byproduct.

[0005] Chinese patent CN111495390B discloses a highly dispersed supported nano-gold catalyst that achieves one-step synthesis of corresponding esters from alcohols using oxygen as an oxidant at temperatures ranging from 50 to 120°C. This method features a simple catalyst preparation process, high reaction selectivity and conversion rate, strong structural stability, excellent resistance to sulfur poisoning, and good compatibility with substrates such as aromatic alcohols, fatty alcohols, and unsaturated alcohols. However, the use of the precious metal gold increases production costs, limiting the industrial application of this method.

[0006] Chinese patent CN117185883B discloses a non-precious metal homogeneous synergistic catalytic system using ferric nitrate nonahydrate as a catalyst and TEMPO (nitrogen oxides) and Lewis acid as co-catalysts. Using oxygen or air as the sole green oxidant, it achieves one-step direct oxidative esterification of various primary alcohols, including aromatic alcohols, fatty alcohols, and heterocyclic alcohols, under mild conditions of 25–60°C and atmospheric pressure, with high selectivity for preparing carboxylic acid esters and good substrate compatibility. Although the raw materials are inexpensive, the homogeneous catalyst is completely miscible with the reaction system, making post-reaction recovery and recycling difficult. This not only increases the cost of raw materials but also introduces an additional burden for subsequent separation.

[0007] In recent years, metal oxides derived from metal-organic frameworks (MOFs) have shown great potential in heterogeneous catalysis due to their advantages such as large specific surface area, abundant active sites, and structural stability. However, cobalt oxides derived solely from ZIF-67 are prone to particle agglomeration or insufficient exposure of active sites during catalysis. Chinese patent CN114797928B discloses a method for preparing Zn-CoO by pyrolysis using ZIF-X@ZIF-Y as a template. x The -CN method can not only effectively inhibit the sintering and agglomeration of cobalt species through physical barrier, but also significantly improve the specific surface area and physicochemical stability of the derived oxides with a high cobalt loading (20~60 wt%).

[0008] Furthermore, N-hydroxyphthalimide, as a highly efficient hydrogen atom transfer catalyst, exhibits unique catalytic properties in the synergistic oxidation of alcohols with Co(II). Currently, no existing technology discloses a method for constructing a synergistic catalytic system using Zn-doped ZIF-67-derived zinc-cobalt composite oxide and N-hydroxyphthalimide for the oxidation of primary alcohols to esters under ambient pressure. Based on this, this invention designs a method for the synergistic oxidation of primary alcohols to esters using Zn-doped modified ZIF-67 calcination-derived zinc-cobalt composite oxide and N-hydroxyphthalimide, aiming to achieve the industrial application of a green and efficient catalytic oxidation method for alcohols to esters. Summary of the Invention

[0009] This invention provides a catalyst, preparation method, and application for the one-pot catalytic oxidation of primary alcohols to esters using oxygen, achieved through Zn doping of a ZIF-67-derived zinc-cobalt composite oxide (abbreviated as Zn-CoO). x The synergistic catalysis of N-hydroxyphthalimide and hydroxyphthalimide results in mild reaction conditions, solving the problems of insufficient economy and environmental protection in traditional methods, as well as the problems of poor catalyst stability, easy passivation of active sites and environmental pollution in traditional oxidation methods. This enables the efficient conversion of primary alcohols to esters under mild conditions.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] The catalyst used for the one-pot catalytic oxidation of primary alcohols to esters is a zinc-cobalt composite oxide, denoted as Zn-CoO, obtained by stepwise calcination of a Zn-doped modified ZIF-67 precursor. x Where x is the stoichiometric coefficient, indicating that cobalt exists simultaneously in both Co(II) and Co(III) valence states in the composite oxide; the zinc-cobalt composite oxide is obtained by stepwise calcination of Zn-doped modified ZIF-67 precursor; the morphology of the Zn-doped modified ZIF-67 precursor is rhombic dodecahedron with a particle size of 0.8~1.2 μm; the obtained Zn-CoO x The morphology is basically maintained as a rhombic dodecahedron with a slightly concave surface and a particle size of 0.8~1.2 μm.

[0012] The method for preparing the catalyst of the present invention includes the following steps:

[0013] (1) Cobalt nitrate hexahydrate and zinc nitrate hexahydrate were dissolved in methanol in the same molar ratio to prepare a homogeneous metal salt solution; 2-methylimidazole was dissolved in methanol to prepare a ligand solution; the two solutions were mixed and magnetically stirred at room temperature until fully mixed, and then allowed to stand for 12-16 h; after the reaction was completed, the purple precipitate generated was collected by centrifugation and washed with methanol and ethanol in sequence; the washed precipitate was dried under vacuum to obtain Zn-doped ZIF-67 precursor powder;

[0014] (2) The Zn-doped ZIF-67 precursor powder was placed in a tube furnace and heated to 450-550℃ under N2 atmosphere at a heating rate, and calcined at a constant temperature for 2-4 h, and then quenched in air to room temperature; then heated to 450-550℃ under air atmosphere at a heating rate, and calcined at a constant temperature for 1-2 h, and then quenched in air to room temperature to obtain the catalyst Zn-CoO x .

[0015] Preferably, in step (1), the molar ratio of cobalt nitrate hexahydrate to zinc nitrate hexahydrate is (20~40):1; the concentration of cobalt nitrate hexahydrate in methanol is 0.15~0.25 mol·L⁻¹. -1 The concentration of 2-methylimidazole in methanol is 0.4–0.5 mol·L⁻¹, calculated as follows: 2-methylimidazole is added at a molar ratio of 4–5:1 to cobalt nitrate hexahydrate and zinc nitrate hexahydrate. -1 ;

[0016] Preferably, in step (1), the washed precipitate is dried under vacuum at 70~80℃ for 12~16 h.

[0017] Preferably, in step (2), the heating rate is 2.0~3.0 ℃·min. -1 .

[0018] The method for preparing esters by one-pot catalytic oxidation of primary alcohols with oxygen using the catalyst of the present invention involves adding the primary alcohol as a reaction substrate to the reaction solvent and adding the catalyst Zn-CoO. x The reaction involves the addition of N-hydroxyphthalimide as a co-catalyst, with oxygen introduced into the solution during the reaction, and the product ester obtained after the reaction is complete.

[0019] Preferably, the molar ratio of the N-hydroxyphthalimide to the primary alcohol substrate is (0.1~0.2):1, and the catalyst is Zn-CoO. x The mass concentration in the reaction solvent is 1~2 g / L -1 The reaction solvent is acetonitrile.

[0020] Preferably, the concentration of the primary alcohol, the reaction substrate, in the reaction solvent is (0.2~0.75) mol·L⁻¹. -1 The primary alcohol of the reaction substrate is selected from one of n-propanol, n-butanol, cyclohexylmethanol, n-octanol or benzyl alcohol.

[0021] Preferably, the ratio of the reaction substrate primary alcohol to the oxygen flow rate is 1 mol : (0.2~0.3) L·min -1 .

[0022] Preferably, the reaction pressure is atmospheric pressure, the reaction temperature is 50~60℃, and the reaction time is 6~12 h.

[0023] This invention designs a zinc-cobalt composite oxide Zn-CoO derived from Zn-doped modified ZIF-67 through stepwise calcination. x A method for the catalytic oxidation of primary alcohols to esters with N-hydroxyphthalimide using oxygen. Compared with the prior art, the present invention has at least the following advantages:

[0024] First, this invention uses oxygen as the sole oxidant, with a reaction temperature of only 50-60℃ under normal pressure. The main byproduct is water, avoiding the use of strong acid catalysts and the generation of large amounts of saline wastewater in the traditional Fischer esterification process. Compared with the nano-gold catalytic system disclosed in Chinese Patent CN111495390B, this invention eliminates the need for precious metals, significantly reducing catalyst costs. Compared with the homogeneous catalytic system disclosed in Chinese Patent CN117185883B, this invention employs a heterogeneous catalyst, Zn-CoO. x After the reaction is complete, it can be easily filtered and separated, overcoming the drawback of homogeneous catalysts being difficult to recover.

[0025] Secondly, this invention exhibits excellent catalytic performance for a variety of typical primary alcohols. The esterification yield of n-propanol reaches 85.6%, n-butanol 97.0%, cyclohexylmethanol 89.9%, n-octanol 80.8%, and benzyl alcohol as high as 96.0%. It demonstrates broad applicability and high selectivity for straight-chain aliphatic primary alcohols, cycloalkyl methanols, and aromatic primary alcohols.

[0026] Third, the catalyst and co-catalyst can be recycled and reused, resulting in good economic efficiency. Zn-CoO x After being recycled five times in the n-butanol oxidative esterification reaction, the catalyst still maintained 96.0% of its catalytic activity (the yield decreased from 97.0% to 93.1%), indicating that the heterogeneous catalyst has excellent stability and recyclability.

[0027] Instruction manual illustrations

[0028] Figure 1 Zn-CoO prepared by Zn doping ZIF-67 x Schematic diagram

[0029] Figure 2 SEM images of ZIF-67-Zn-1

[0030] Figure 3 Zn-CoO x SEM image of -1 Specific implementation methods

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention. The technical solutions of the present invention are described in detail below with reference to the embodiments, but the scope of protection is not limited thereto. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] The embodiments of the present invention are as follows:

[0033] catalyst Zn-CoO x This is a zinc-cobalt composite oxide obtained by stepwise calcination of a Zn-doped modified ZIF-67 precursor. The morphology of the Zn-doped modified ZIF-67 precursor is rhombic dodecahedral with a particle size of 0.8~1.2 μm; the resulting Zn-CoO x The morphology is basically maintained as a rhombic dodecahedron, with a slightly concave surface structure and a particle size of 0.8~1.2 μm, such as... Figure 1 As shown.

[0034] The catalyst Zn-CoO x The preparation method includes the following steps:

[0035] (1) Cobalt nitrate hexahydrate and zinc nitrate hexahydrate are dissolved together in methanol at a molar ratio of (20~40):1 to prepare a homogeneous solution of the metal salt, wherein the concentration of cobalt nitrate hexahydrate in methanol is 0.15~0.25 mol·L. -1 A ligand solution was prepared by dissolving 2-methylimidazole in methanol at a total molar ratio of 4-5:1 to cobalt nitrate hexahydrate and zinc nitrate hexahydrate, wherein the concentration of 2-methylimidazole in methanol was 0.4-0.5 mol·L⁻¹. -1 The two solutions were mixed and stirred magnetically at room temperature until fully mixed, and then allowed to stand for 12-16 h. After the reaction was completed, the purple precipitate was collected by centrifugation and washed with methanol and ethanol in sequence. The washed precipitate was dried under vacuum at 70-80℃ for 12-16 h to obtain Zn-doped ZIF-67 precursor powder.

[0036] (2) The Zn-doped ZIF-67 precursor powder was placed in a tube furnace and heated at 2.0~3.0 ℃·min under a N2 atmosphere. -1 The temperature was increased to 450–550 °C at a heating rate, and calcined at this rate for 2–4 h. The sample was then rapidly removed and quenched to room temperature in air. Finally, it was heated in air at a rate of 2.0–3.0 °C / min. -1 The temperature was increased to 450-550℃ at a heating rate, and calcined at this temperature for 1-2 hours. The sample was then immediately removed and quenched in air to room temperature to obtain the catalyst Zn-CoO. x .

[0037] The one-pot catalytic oxidation of primary alcohols with oxygen to prepare esters is as follows: The primary alcohol substrate is added to the reaction solvent, followed by the catalyst Zn-CoO2. x The reaction involves the use of N-hydroxyphthalimide as a co-catalyst, with oxygen introduced into the solution during the reaction. After the reaction is complete, the product ester is obtained by separation.

[0038] Furthermore, the molar ratio of the N-hydroxyphthalimide to the primary alcohol substrate is (0.1~0.2):1, and the Zn-CoO x The mass concentration in the reaction solvent is 1~2 g / L -1 .

[0039] Furthermore, the reaction solvent is acetonitrile.

[0040] Furthermore, the concentration of the primary alcohol, the reaction substrate, in the reaction solvent is (0.2~0.75) mol·L⁻¹. -1 .

[0041] Furthermore, the ratio of the primary alcohol substrate to the oxygen flow rate is 1 mol : (0.2~0.3) L·min -1 .

[0042] Furthermore, the primary alcohol of the reaction substrate is selected from one of n-propanol, n-butanol, cyclohexylmethanol, n-octanol, or benzyl alcohol.

[0043] Furthermore, the reaction pressure is atmospheric pressure, the reaction temperature is 50~60℃, and the reaction time is 6~12 h.

[0044] Furthermore, after the reaction is complete, Zn-CoO is separated by filtration. x The product is washed with ethanol and dried in a vacuum drying oven for reuse. The co-catalyst N-hydroxyphthalimide can be precipitated and recovered by vacuum rotary evaporation, and the solvent and product ester are separated by further rotary evaporation.

[0045] Example 1

[0046] This example demonstrates the catalytic oxidation of n-propanol to prepare n-propyl propionate:

[0047] Catalyst preparation:

[0048] 2.91 g of cobalt nitrate hexahydrate and 0.149 g of zinc nitrate hexahydrate were dissolved in 50 mL of methanol to prepare a homogeneous metal salt solution; 3.45 g of 2-methylimidazole was dissolved in 100 mL of methanol to prepare a ligand solution. The two solutions were mixed and magnetically stirred thoroughly at room temperature, then allowed to stand for 12 h. After the reaction was complete, the resulting purple precipitate was collected by centrifugation and washed twice each with methanol and ethanol. The washed precipitate was dried under vacuum at 70 °C for 12 h to obtain the Zn-doped ZIF-67 precursor powder ZIF-67-Zn-1, the SEM image of which is shown below. Figure 2 As shown. ZIF-67-Zn-1 was placed in a tube furnace and heated at 2.0℃ for min under a N2 atmosphere. -1 The temperature was increased to 450℃ at a heating rate, and calcined at this rate for 2 hours. The sample was then immediately removed and quenched to room temperature. It was then further calcined in air at a rate of 2.0℃ / min. -1 The temperature was increased to 450℃ at a heating rate, and calcined at that temperature for 1 h. The sample was then immediately removed and quenched to room temperature to obtain the catalyst Zn-CoO. x -1, its SEM image is as follows Figure 3 As shown.

[0049] Oxidative esterification reaction:

[0050] Add 10 mL of acetonitrile, 2 mmol (0.2 mol L) -1n-Propanol, 0.2 mmol N-hydroxyphthalimide, 10 mg Zn-CoO x -1 was added to a 25 mL two-necked flask and, under normal pressure, was pumped at a rate of 0.4 mL / min. -1 Oxygen was introduced at a rate of 0.5%, and the mixture was stirred at a constant temperature of 50°C for 6 h. After the reaction was completed, gas chromatography was used to detect the final product, which was determined to be n-propyl propionate with a yield of 85.6%.

[0051] Example 2

[0052] This example demonstrates the preparation of n-butyl butyrate via the catalytic oxidation of n-butanol.

[0053] Catalyst preparation:

[0054] 2.91 g of cobalt nitrate hexahydrate (Co(NO3)2・6H2O) and 0.087 g of zinc nitrate hexahydrate (Zn(NO3)2・6H2O) were dissolved together in 50 mL of methanol to prepare a homogeneous metal salt solution; 3.7 g of 2-methylimidazole was dissolved in 100 mL of methanol to prepare a ligand solution. The two solutions were mixed and magnetically stirred thoroughly at room temperature, then allowed to stand for 16 h. After the reaction was complete, the resulting purple precipitate was collected by centrifugation and washed twice each with methanol and ethanol. The washed precipitate was dried under vacuum at 80 °C for 16 h to obtain Zn-doped ZIF-67 precursor powder ZIF-67-Zn-2. ZIF-67-Zn-2 was placed in a tube furnace and dried at 2.5 °C for 1 min under N2 atmosphere. -1 The temperature was increased to 500℃ at a certain heating rate, and calcined at this temperature for 3 hours. The sample was then immediately removed and quenched to room temperature. It was then further calcined in air at 2.5℃ for 1 minute. -1 The temperature was increased to 500℃ at a heating rate, and calcined at this temperature for 1.5 h. The sample was then immediately removed and quenched to room temperature to obtain the catalyst Zn-CoO. x -2.

[0055] Oxidative esterification reaction:

[0056] Add 10 mL of acetonitrile, 2 mmol (0.2 mol L) - ¹) n-Butanol, 0.3 mmol N-hydroxyphthalimide, 20 mg Zn-CoO x -2 was added to a 25 mL double-necked flask and, under normal pressure, was pumped at 0.4 mL / min. -1 Oxygen was introduced at a rate of 0.5%, and the mixture was stirred at a constant temperature of 50°C for 9 h. After the reaction was completed, gas chromatography was used to detect the final product, which was determined to be n-butyl butyrate, with a yield of 97.0%.

[0057] Example 3

[0058] This example demonstrates the preparation of n-butyl butyrate via the catalytic oxidation of n-butanol.

[0059] The catalyst used in Example 2 was selected.

[0060] Oxidative esterification reaction:

[0061] Add 500 mL of acetonitrile and 250 mmol (0.5 mol L) - ¹) n-Butanol, 50 mmol N-hydroxyphthalimide, 500 mg Zn-CoO x -2 was added to a 1000 mL three-necked flask and, under normal pressure, was pumped at a rate of 50 mL / min. -1 Oxygen was introduced at a rate of 0.5%, and the mixture was stirred at a constant temperature of 50°C for 12 h. After the reaction was completed, gas chromatography was used to detect the final product, which was determined to be n-butyl butyrate, with a yield of 92.4%.

[0062] Example 4

[0063] This example demonstrates the catalytic oxidation of cyclohexyl methanol to prepare cyclohexylmethyl formate:

[0064] Catalyst preparation:

[0065] 3.64 g of cobalt nitrate hexahydrate and 0.093 g of zinc nitrate hexahydrate were dissolved in 50 mL of methanol to prepare a homogeneous metal salt solution; 5.3 g of 2-methylimidazole was dissolved in 125 mL of methanol to prepare a ligand solution. The two solutions were mixed and magnetically stirred thoroughly at room temperature, then allowed to stand for 16 h. After the reaction was complete, the resulting purple precipitate was collected by centrifugation and washed twice each with methanol and ethanol. The washed precipitate was dried under vacuum at 80 °C for 14 h to obtain the Zn-doped ZIF-67 precursor powder ZIF-67-Zn-3. ZIF-67-Zn-3 was placed in a tube furnace and dried at 3.0 °C for 1 min under a N2 atmosphere. -1 The temperature was increased to 550℃ at a heating rate, and calcined at this rate for 4 hours. The sample was then immediately removed and quenched to room temperature. It was then further calcined in air at 3.0℃ for 1 minute. -1 The temperature was increased to 550℃ at a heating rate, and calcined at that temperature for 2 hours. The sample was then immediately removed and quenched to room temperature to obtain the catalyst Zn-CoO. x -3.

[0066] Oxidative esterification reaction:

[0067] Add 10 mL of acetonitrile, 2 mmol (0.2 mol L) - ¹) Cyclohexylmethanol, 0.2 mmol N-hydroxyphthalimide, 10 mg Zn-CoO x-3 was added to a 25 mL double-necked flask and, under normal pressure, was pumped at 0.4 mL / min. -1 Oxygen was introduced at a rate of 0.5%, and the mixture was stirred at a constant temperature of 60°C for 12 h. After the reaction was completed, gas chromatography was used to detect the final product, which was determined to be cyclohexylmethyl cyclohexylcarboxylate, with a yield of 89.9%.

[0068] Example 5

[0069] This example demonstrates the catalytic oxidation of n-octanol to prepare n-octyl octanoate:

[0070] The catalyst used in Example 1 was selected.

[0071] Oxidative esterification reaction:

[0072] Add 10 mL of acetonitrile, 2 mmol (0.2 mol L) - ¹) n-Octanol, 0.2 mmol N-hydroxyphthalimide, 10 mg Zn-CoO x -1 was added to a 25 mL two-necked flask and, under normal pressure, was pumped at a rate of 0.6 mL / min. -1 Oxygen was introduced at a rate of 100%, and the mixture was stirred at a constant temperature of 60°C for 12 h. After the reaction was completed, gas chromatography was used to detect the final product, which was determined to be n-octanoic acid n-octanoate, with a yield of 80.8%.

[0073] Example 6

[0074] This example demonstrates the catalytic oxidation of benzyl alcohol to prepare benzoic acid ester:

[0075] The catalyst used in Example 4 was selected.

[0076] Oxidative esterification reaction:

[0077] Add 10 mL of acetonitrile, 2 mmol (0.2 mol L) - ¹) Benzyl alcohol, 0.2 mmol N-hydroxyphthalimide, 10 mg Zn-CoO x -3 was added to a 25 mL double-necked flask and, under normal pressure, was pumped at 0.4 mL / min. -1 Oxygen was introduced at a rate of 0.5%, and the mixture was stirred at a constant temperature of 60°C for 12 h. After the reaction was completed, gas chromatography was used to detect the final product, which was determined to be benzoic acid ester, with a yield of 96.0%.

[0078] Example 7

[0079] This example demonstrates catalyst cycle performance testing.

[0080] Using the reaction system of Example 2, the Zn-CoO2 separated and recovered after the reaction was... x-2 (washed with ethanol and vacuum dried) was repeatedly used in the n-butanol oxidation reaction, with each reaction under the same conditions as in Example 2. The product yield was recorded as follows: 97.0% for the first use, 94.5% for the second, 94.2% for the third, 93.7% for the fourth, and 93.1% for the fifth. After five cycles, the catalytic activity remained at 96.0%, indicating that Zn-CoO x -2 exhibits good stability and cyclic reuse performance.

[0081] Example 8

[0082] This example demonstrates the cycling performance test of the co-catalyst and solvent:

[0083] Using the reaction system of Example 2, the N-hydroxyphthalimide and acetonitrile recovered after the reaction were reused for the n-butanol oxidation reaction. The reaction conditions were the same as in Example 2: the yield was 97.0% for the first use, 95.3% for the second, 93.8% for the third, 92.5% for the fourth, and 91.7% for the fifth. After five cycles, the product yield decreased by no more than 5.5%, indicating that the recycling performance of N-hydroxyphthalimide and acetonitrile was good.

[0084] The above description is a further detailed explanation of the present invention in conjunction with specific preferred embodiments. However, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A catalyst for the one-pot catalytic oxidation of primary alcohols to esters using oxygen, characterized in that it is... The zinc-cobalt composite oxide obtained by stepwise calcination of Zn-doped ZIF-67 precursor is denoted as Zn-CoO. x Where x is the stoichiometric coefficient, indicating that cobalt exists simultaneously in both Co(II) and Co(III) valence states in the composite oxide; the zinc-cobalt composite oxide is obtained by stepwise calcination of Zn-doped modified ZIF-67 precursor; the morphology of the Zn-doped modified ZIF-67 precursor is rhombic dodecahedron with a particle size of 0.8~1.2 μm; the obtained Zn-CoO x The morphology is basically maintained as a rhombic dodecahedron with a slightly concave surface and a particle size of 0.8~1.2 μm.

2. The method for preparing the catalyst according to claim 1, characterized in that, Includes the following steps: (1) Cobalt nitrate hexahydrate and zinc nitrate hexahydrate were dissolved in methanol in the same molar ratio to prepare a homogeneous metal salt solution; 2-methylimidazole was dissolved in methanol to prepare a ligand solution; the two solutions were mixed and magnetically stirred at room temperature until fully mixed, and then allowed to stand for 12-16 h; after the reaction was completed, the purple precipitate generated was collected by centrifugation and washed with methanol and ethanol in sequence; the washed precipitate was dried under vacuum to obtain Zn-doped ZIF-67 precursor powder; (2) The Zn-doped ZIF-67 precursor powder was placed in a tube furnace and heated to 450-550℃ under N2 atmosphere at a heating rate, and calcined at a constant temperature for 2-4 h, and then quenched in air to room temperature; then heated to 450-550℃ under air atmosphere at a heating rate, and calcined at a constant temperature for 1-2 h, and then quenched in air to room temperature to obtain the catalyst Zn-CoO x .

3. The method for preparing the catalyst according to claim 1, characterized in that, In step (1), the molar ratio of cobalt nitrate hexahydrate to zinc nitrate hexahydrate is (20~40):1; the concentration of cobalt nitrate hexahydrate in methanol is 0.15~0.25 mol·L⁻¹. -1 The concentration of 2-methylimidazole in methanol was 0.4–0.5 mol·L⁻¹, with a molar ratio of 4–5:1 to the total molar amounts of cobalt nitrate hexahydrate and zinc nitrate hexahydrate. -1 .

4. The method for preparing the catalyst according to claim 1, characterized in that, In step (1), the washed precipitate is dried under vacuum at 70-80°C for 12-16 h.

5. The method for preparing the catalyst according to claim 1, characterized in that, In step (2), the heating rate is 2.0~3.0 ℃·min. -1 .

6. A method for preparing esters by one-pot catalytic oxidation of primary alcohols with oxygen using the catalyst of claim 1, characterized in that, The primary alcohol, the reaction substrate, is added to the reaction solvent, along with the catalyst Zn-CoO. x The reaction involves the addition of N-hydroxyphthalimide as a co-catalyst, with oxygen introduced into the solution during the reaction, and the product ester obtained after the reaction is complete.

7. The one-pot catalytic oxidation of primary alcohols with oxygen to prepare esters as described in claim 6, characterized in that, The molar ratio of N-hydroxyphthalimide to the primary alcohol substrate is (0.1~0.2):1, and the catalyst is Zn-CoO. x The mass concentration in the reaction solvent is 1~2 g / L -1 The reaction solvent is acetonitrile.

8. The method for preparing esters by one-pot catalytic oxidation of primary alcohols with oxygen using a catalyst as described in claim 6, characterized in that, The concentration of the primary alcohol, the reaction substrate, in the reaction solvent is (0.2~0.75) mol·L⁻¹. -1 The primary alcohol substrate is selected from one of n-propanol, n-butanol, cyclohexylmethanol, n-octanol, or benzyl alcohol.

9. The method for preparing esters by one-pot catalytic oxidation of primary alcohols with oxygen using a catalyst as described in claim 6, characterized in that, The ratio of the primary alcohol substrate to the oxygen flow rate is 1 mol : (0.2~0.3) L·min. -1 .

10. The one-pot catalytic oxidation of primary alcohols with oxygen to prepare esters as described in claim 6, characterized in that, The reaction pressure is atmospheric pressure, the reaction temperature is 50~60℃, and the reaction time is 6~12 h.

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